It is often desirable to study the effect of environmental exposure on FRP bars under a stressed state while embedded in concrete. This requires investigating the behavior of structural elements reinforced with FRP bars and involves large scale materials and labor. Further the transportation of such specimens for environmental exposure is difficult. In addition, because of the high strength of FRP bars, the testing of such reinforcing bars up to failure requires large spans and a high magnitude of gravity loads.
In view of the aforementioned difficulties, long-term durability studies under stressed state representing the actual exposure of loading are not widely reported in the literature. However, a patent search did disclose a U.S. Patent of Kitta et al. U.S. Pat. No. 4,648,224. As disclosed therein, a tendon for prestressed concrete wherein inorganic particles are coated on an outer surface of a rod made of fiber reinforced plastic through a plastic adhesive layer. The inorganic particles are formed with minute rugged surface portions on the outer surface of the tendon for prestressed concrete, the rugged surface portions being firmly adhered to concrete. The inorganic particles are coated on the whole outer surface of the tendon for prestressed concrete, on the fixed portions at both ends, and on a portion subjected to the maximum bending moment. The reference teaches that samples are prestressed to 70% of the breaking load in a mold and concrete introduced into the mold. After hardening, prestressing grips are released and a strain gauge on the surface of the concrete measures surface strain at various points.
A more recent U.S. Pat. No. 7,056,463 of Ohta discloses a method of manufacturing prestressed concrete. As disclosed, pre-tension and post-tension processes for the manufacture of pre-stressed structures in which bonded carbon fiber cables are provided with burial anchors and temporary anchors outward of the burial anchors. The burial anchors are embedded in the structure. The temporary anchors enable stressing of the carbon fiber cables.
It is presently believed that the present invention provides a solution to the above-identified problems by developing a new apparatus for preparing representative small size specimens for testing FRP bars embedded in concrete under a stressed state and during relatively long-term environmental exposure. The desired stress level in FRP bars can be easily maintained during the period of investigation.